TRANSFER OF A MOBILE UNIT COMPATIBLE WITH PREVIOUS VERSIONS
FIELD OF THE INVENTION This invention generally relates to communication systems, and, more particularly, to wireless communication systems. BACKGROUND OF THE INVENTION The coverage area of a wireless communication system is typically divided into a number of cells, which can be grouped into one or more networks. The base stations associated with the cells provide wireless connectivity to mobile units in the cell or in a sector of the cell. The mobile units may include devices such as mobile phones, personal data assistants, smart phones, Global Positioning System devices, wireless network interface cards, desktop or laptop computers, and the like. The mobile units located in each cell can access the wireless communication system by establishing a wireless communication link, often referred to as an air interface, with a base station associated with the cell. The information can be transmitted on the air interface by using a carrier, such as a high-frequency wave-shaped sinusoid that is modulated based on
Ref. 197786 the information to be transmitted by the carrier. Each base station can support more than one carrier and mobile units located in a specific position may be able to access carriers provided by more than one base station. Mobile units are often transferred from one base station to another and / or from one carrier to another. For example, a mobile unit can wander through multi-cell coverage areas and can therefore be transferred from one base station to another while the mobile unit travels through the associated cells or sectors. As another example, the coverage area associated with a base station and / or a carrier may vary due to changing environmental conditions, changing network configurations, and the like. By . consequently, even stationary mobile units can be transferred to another base station, for example, if the channel quality provided by the current service base station deteriorates. Handovers can be hard, that is, the old connection to the base service station is broken before the new connection is made to a target base station, or soft, that is, the new connection is made to the target base station before that the old connection to the service base station is broken. In this way, a mobile unit in soft handover maintains concurrent connections with more than one base station during the handover.
The changing wireless communication systems frequently include cells that provide wireless connectivity using carriers that operate in accordance with different revisions or versions of the relevant wireless communication standards. For example, a conventional wireless communication system may include some base stations that operate in accordance with Revision-B and / or Revision-C of the CDMA (EVDA) standards of 2000 CDMA (for its acronym in English) The Revision-C is a revision after Revision-B and thus the mobile units that support Revision-B may or may not support Revision-C, and vice versa. When a mobile unit is transferred in a conventional wireless communication system, the mobile unit will attempt to transfer to a carrier operating in accordance with the most recent revision supported by the mobile unit. For example, a mobile unit that supports Revision-C will always try to transfer to a bearer that also operates in accordance with Revision-C. The transfer to carriers operating in accordance with the most recent revision has a number of advantages, such as allowing the mobile unit to use the enhanced services provided by the most recent revision. Nevertheless, this approach also has a number of disadvantages. For example, many mobile units may attempt to transfer carriers operating in accordance with the most recent revision, at least in part due to the aforementioned advantages for using these carriers. As a result, these carriers may become overloaded or not available. The total quality of service provided to mobile units that transmit on carriers that operate in accordance with the most recent revision may degrade when these carriers become overloaded. In addition, scarce radio resources may be wasted when additional mobile units attempt to transfer overloaded or unavailable carriers. SUMMARY OF THE INVENTION The present invention is directed to addressing the effects of one or more of the above problems. The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an exhaustive review of the invention. It is not intended to identify key or critical elements of the invention nor to outline the scope of the invention. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is discussed later. In one embodiment of the present invention, there is provided a method for wireless communication involving at least one first carrier operating in accordance with a first type of system and at least one second carrier operating in accordance with a second type of system. The method may include determining that a mobile unit is to be transferred between a first carrier operating in accordance with the first type of system and a second carrier operating in accordance with the second type of system based on a load of at least one the first and second carriers. BRIEF DESCRIPTION OF THE DRAWINGS The invention can be understood by reference to the following description taken in conjunction with the accompanying figures, in which like reference numbers identify similar elements, and wherein: Figure 1 conceptually illustrates an illustrative embodiment of a communication system wireless, in accordance with the present invention; Figure 2 conceptually illustrates an illustrative embodiment of an attached information message, in accordance with the present invention; and Figure 3 conceptually illustrates an illustrative embodiment of a handover method for a mobile unit, in accordance with the present invention. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof were shown by way of example in the figures and are described herein in detail. However, it should be understood that the description of specific embodiments herein is not intended to limit the invention to the particular forms described, but rather, the intention is to cover all modifications, equivalents, and alternatives that fall within the spirit and scope of the invention. the invention as defined by the appended claims. DETAILED DESCRIPTION OF THE INVENTION Illustrative embodiments of the invention are described below. In the interest of clarity, not all aspects of an actual implementation are described in this specification. Of course it will be appreciated that in the development of any such real mode, numerous specific implementation decisions must be made to achieve the specific goals of the developers, such as compliance with the system-related and business-related constraints, which will vary from one implementation to another. to another. In addition, it will be appreciated that such a development effort can be complex and time consuming, but will nonetheless be a routine task for those skilled in the art who have the benefit of this description. The portions of the present invention and corresponding detailed description are presented in terms of software, or algorithms and symbolic representations of operations in data bits within a computer memory. These descriptions and representations are those by which an expert in the art effectively transports the essence of his work to other experts in the art. An algorithm, as the term is used here, and as it is generally used, is conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those that require physical manipulations of physical quantities. Usually, but not necessarily, these quantities take the form of optical, electrical, or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. At some moments it was convenient, mainly for reasons of common use, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. However, it must be kept in mind that all these terms and the like will be associated with the appropriate physical quantities and are simply convenient labels applied to those quantities. Unless specifically mentioned otherwise, or as is evident from the discussion, terms such as "processing" or "computation" or "calculating" or "determining" or "presenting" or the like, refer to the action and procedures of a computer system, or similar electronic computing device, that manipulates and transforms data represented as electronic, physical quantities within the records and memories of the computer system into other data similarly represented as physical quantities within the memories or records of the computer system or other such storage, transmission or presentation of information devices. It should also be noted that the software implemented aspects of the invention are typically encoded in some form of program storage medium or implemented in some form of transmission medium. The program storage medium can be magnetic (for example, a floppy disk or a hard drive) or optical (for example, a read-only memory compact disk, or "CD ROM"), and can be read only or random access. Similarly, the transmission medium may be pairs of twisted cable, coaxial cable, optical fiber, or some other suitable transmission means known in the art. The invention is not limited by these aspects of any given implementation. The present invention will now be described with reference to the appended figures. Various structures, systems and devices are illustrated schematically in the figures for the purpose of explanation only and not to obscure the present invention with details that are well known to those skilled in the art. However, the appended figures are included to describe and explain illustrative examples of the present invention. The words and phrases used herein should be understood and interpreted to have a meaning consistent with the understanding of those words and phrases by those skilled in the relevant art. No special definition of a term or phrase, ie, a definition that is different from the ordinary and common meaning as understood by those skilled in the art, is intended to be implied by consistent use of the term or phrase herein. To the extent that a term or phrase is intended to have a special meaning, ie, a different meaning understood by skilled in the art, such a special definition expressly exhibited in the specification in a manner on definition given directly and unequivocally defining Special for the term or phrase. Figure 1 conceptually illustrates a first illustrative embodiment of a wireless communication system 100. In the illustrated embodiment, the wireless communication system 100 provides wireless communication to a plurality of geographic areas or cells 105 (1-2), 110 (1- 4). Numerical indices may fall when cells 105, 110 are referenced collectively. However, the numerical indices (1-2), (1-4) can be used to indicate individual cells 105, 110 and / or subgroups of cells 105, 110. This numbering convention can be applied to elements illustrated in other figures and distinguished by different numerical indexes. Experts in the art who have the benefit of the present disclosure should appreciate that wireless connectivity can be provided to cells 105, 110 using one or more base stations, base station routers, access points, and the like, as well as controllers such as radio network controllers, although these entities and / or devices are not shown in Figure 1. Experts in the art having the benefit of the present disclosure should also appreciate that the number of cells 105, 110 shown in Figure 1 is intended to be illustrative and not limit the present invention. The cells 105, 110 are separated into layers 115, 120 that implement different types of system. In one embodiment, the system types implemented in the layers 115, 120 are distinguished by the standard or protocol revision used to provide wireless connectivity over the carriers supported by the cells in the layers 115, 120. For example, the layer 115 can operate in accordance with Revision-C of the EVDO standard and layer 120 may operate in accordance with Revision-B of the EVDO standard. As used herein, the terms "standard or protocol revision" shall be understood to refer to revisions of a wireless communication standard or protocol that are implemented in (or support for) successive generations of wireless communication equipment. A feature of a standard or protocol review is that wireless communication equipment that was originally designed only to support a previous, or legacy, review is typically not able to communicate when using subsequent (or newer) revisions of the standard or protocol . In contrast, the wireless communication equipment that was designed to support subsequent revisions may also be able to support legacy revisions of the standard or protocolFor example, wireless communication equipment may be compatible with previous versions with legacy reviews of standards or protocols. The system types implemented in layers 115, 120 can also be distinguished by frequencies of the carriers used to provide wireless connectivity and / or the radio access technology used to provide wireless connectivity. For example, in a wireless communication system 100 operating in accordance with EVDO Review-B standards and / or protocols, wireless connectivity can be provided to cells 105 that use a first carrier frequency and to cells 110 that use a second carrier frequency. As another example, wireless connectivity can be provided to cells 105 in accordance with U TS standards and / or protocols and wireless connectivity can be provided to cells 110 in accordance with standards and / or revision protocols. -C of EVDO. The wireless communication system 100 provides wireless connectivity to one or more mobile units 125. Only one mobile unit 125 is shown in the illustrated mode, however, those skilled in the art having the benefit of the present disclosure should appreciate that any number of mobile units 125 may operate within wireless communication system 100. Experts in the art who have the benefit of the present disclosure should also appreciate that mobile units 125 may refer to using other terms of the art such as "user equipment" , "mobile stations", "subscriber units", "subscriber stations", and the like. Illustrative mobile units 125 may include, but are not limited to, devices such as mobile phones, personal data assistants, smart phones, Global Positioning System devices, wireless network interface cards, portable desktop computers, and the like. The mobile unit 125 may be able to communicate with cells 105, 110 in one or both of the layers 115, 120. For example, the mobile unit 125 may be a revision-C EVDO device compatible with earlier versions that is capable of communicate by using carriers provided by cells 105 in accordance with the EVDO Standard-C revision and carriers provided by cells 110 in accordance with EVDO Standard-revision-B. As another example, the mobile unit 125 may be an EVDO Revision-B device that is not capable of communicating when using carriers provided by cells 105 in accordance with Revision-C of the EVDO standard, but is able to communicate to the use carriers provided by cells 110 in accordance with Revision-B of the EVDO standard. In the illustrated embodiment, the mobile unit 125 is displayed in a location that is associated with the coverage areas that overlap the cells 105 (1), 110 (3). The mobile unit 125 can therefore be transferred between carriers provided by the cells 105 (1), 110 (3). A controller such as a radio network controller (not shown) can determine whether or not to transfer the mobile unit 125 based on loads associated with the carriers provided by the cells 105 (1), 110 (3). In one embodiment, the transfer decision can be used to support service degrees (GoS) in the wireless communication system 100. For example, cells 105 can support a more recent revision of a standard or protocol, such as Revision-C, and cells 110 can support a legacy revision of the standard or protocol, such as Revision-B. If the carriers in cell 105 (1) are heavily loaded or overloaded, but additional emergency calls and / or high priority calls attempting to access these carriers, then non-emergency calls and / or lower priority calls than currently communicate when using these carriers can be transferred to carriers in cell 110 (3). The decision to degrade one or more lower priority calls may also be, based on the quality of service required for emergency calls and / or high priority calls, as well as a projected load of carriers after admission of priority calls. Alternatively, if the mobile unit 125 has a connection using a carrier in the cell 110 (3) but the load of carriers in the cell 105 (1) is relatively low, the mobile units 125 can be transferred from the cell 110 (3) to cell 105 (1). The handover of the mobile unit 125 between carriers operating in accordance with different types of system, such as different revisions of a standard or protocol, may require the mobile unit 125 to change a personality or profile. As used herein and in accordance with use in the art, the term "personality" will be understood to refer to information and / or algorithms stored and / or used by the mobile unit 125 to establish communications on a bearer in accordance with the standards and / or protocols implemented by the carrier. For example, the personality of the mobile unit 125 may include configuration information used to configure the mobile unit 125 to communicate in accordance with the standards and / or protocols implemented by the bearer, such as Revision-B and / or Revision-C. The personality can be implemented in hardware, programming in firmware, software, or any combination thereof. In one embodiment, a handover in cell 110 (3) to cell 105 (1) can be triggered by handover from cell 110 (2) to cell 110 (3). For example, mobile unit 125 may initially be associated with cell 110 (2). The mobile unit 125 can therefore access the wireless communication system 100 through the cell 110 (2) and receive information from the wireless communication system 100 through the cell 110 (2), for example, in accordance with Revision-B of the EVDO standard. The mobile unit 125 can then be moved in a geographical area or sector served by the superimposed carriers 105 (1), 110 (3). Performing a hard handover of cell 110 (2) operating in accordance with the first type of system to cell 105 (1) operating in accordance with the second type of system may result in performance degradation compared to performing a handover soft. Accordingly, a soft handover can first be used to pass the mobile unit 125 of the cell 110 (2) to the cell 110 (3). The soft handover is followed by the handover of the mobile unit 125 from the cell 110 (3) to the cell 105 (1), which may occur after the mobile unit 125 moved towards the center of the cell 110 (3) and This can reduce performance degradation. In one embodiment, the mobile unit 125 may receive one or more enclosing information messages provided by the predetermined bearer 110 (3) (i.e., the bearer currently serving the mobile unit 125) prior to (or during) handover. The attached information message (s) includes (n) a list of carriers and system types associated with these carriers. For example, the attached information message may include a list of one or more carriers compatible with Revision-C and one or more carriers compatible with Revision-B. In one embodiment, the attached information message may also include information indicating whether the listed carriers are available or not for given priority classes of mobile units, for example, the list may indicate whether the carriers are currently overloaded. Figure 2 conceptually illustrates an illustrative embodiment of an attached information message 200. In the illustrated embodiment, the attached information message 200 includes a field 205 indicating a total number of carriers in the sector receiving the attached information message 200. The attached information message 200 also includes a group of fields 210, 215, 220 for each of the existing carriers. The fields 215, 220 indicate the carrier band class and the CDMA channel or bearer carrier number, respectively. Field 210 indicates the type of system of the associated bearer. For example, field 210 may indicate that the associated bearer operates in accordance with Revision-B or Revision-C of the EVDO standard. However, as discussed above, the fields 210 may also indicate other types of system associated with the bearer. In one embodiment, the attached information message 200 includes a field 225 indicating availability of the associated bearer. For example, field 225 may include information indicating whether the carrier is overloaded. Alternatively, field 225 may include information indicating a current load of the carrier with different levels of availability associated with different priority classes of mobile units. Instead of field 225, another possible way of transporting bearer availability information to mobile units is to define a field, such as an Access Cryptographic Summary Channel Mask field, in the attached DO information message (for its acronyms in English) for this purpose. Figure 3 conceptually illustrates an illustrative embodiment of a method 300 for handover of a mobile unit. In the illustrated embodiment, one or more access networks (ANs) (or constituent base stations) monitor (at 305) load carriers associated with overlapping wireless communication systems. For example, access networks may monitor (at 305) carriers associated with a first layer of cells operating in accordance with a first type of system, such as a more recent revision of a standard or protocol, and carriers associated with a second one. layer of cells operating in accordance with a second type of system, such as a legacy revision of the standard or protocol. In some modalities, the first layer and the second layer of the cells can cover the same geographical area. If the access network determines (at 310) that a carrier in the first layer of cells, for example a Revision-C bearer, is overloaded, and the access network can determine (in 315) whether any of the other carriers in the first layer of cells is available in the same geographical coverage area. The mobile units can be transferred (at 320) to other carriers in the first cell layer, if the access network determines (at 315) that the other carriers (relatively lightly charged) are available. For example, relatively low priority users who are not currently in soft transfer and measured relatively strong signal-to-noise ratios can be directed to transfer to other carriers. However, if the access network determines (at 315) that other carriers are not available in the first cell layer, then one or more mobile units can be directed to transfer (at 325) carriers in the second cell layer, such as carriers that operate in accordance with standards or legacy protocols such as Revision-B. The mobile units can also lead (in 325) a personality degradation in response to being transferred (in 325) to one of the carriers in the second layer of cells. If the access network determines (at 310) that a bearer in the first layer of cells, for example a Revision-C bearer, is not overloaded, then the mobile units in other bearers may be transferred to the bearer in the first layer of cells . In the illustrated mode, the access network can determine (at 330) that any other of the mobile units compatible with previous versions (or access terminals, ATs) currently have a communication link in an associated carrier with the second layer of cells, for example a Revision-B bearer, if the access network identifies (in 330) a mobile unit compatible with eligible previous versions, the access network can determine (at 335) whether the currently eligible mobile unit is in soft handoff and measured a relatively strong signal-to-noise ratio of the pilot. If the mobile unit is currently in soft handoff and / or measured a relatively weak signal-to-noise ratio, then the access network may continue to search (in 330) other mobile units compatible with eligible prior versions. Mobile units compatible with eligible prior versions that are not currently in soft transfer and measured a relatively strong signal-to-noise ratio can be transferred (at 340) to a carrier in the first cell layer. For example, mobile units compatible with eligible prior versions can be transferred (at 340) to a Revision-C bearer in the first layer of cells from bearers in the second layer of cells, such as bearers operating in accordance with standards or protocols of legacy such as Revision-B. In one embodiment, the personality of the eligible mobile unit compatible with previous eligible versions can change (by 340) in response to transferring (at 340) the mobile unit to the bearer in the first cell layer. The particular embodiments described above are illustrative only, since the invention can be modified and practiced in different but equivalent ways evident to those skilled in the art having the benefit of the teachings herein. In addition, no limitations are intended to the details of construction or design shown herein, other than those described in the claims below. It is therefore evident that the particular embodiments described above can be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought here is as set forth in the subsequent claims. It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention.